Re: [PATCH 0/5] drm/bridge: samsung-dsim: fix various modes with ADV7535 bridge

[Adam Ford]

On Mon, Aug 28, 2023 at 11:13 AM Adam Ford <aford173@xxxxxxxxx> wrote:
>
> On Mon, Aug 28, 2023 at 10:59 AM Michael Tretter
> <m.tretter@xxxxxxxxxxxxxx> wrote:
> >
> > I tested the i.MX8M Nano EVK with the NXP supplied MIPI-DSI adapter,
> > which uses an ADV7535 MIPI-DSI to HDMI converter. I found that a few
> > modes were working, but in many modes my monitor stayed dark.
> >
> > This series fixes the Samsung DSIM bridge driver to bring up a few more
> > modes:
> >
> > The driver read the rate of the PLL ref clock only during probe.
> > However, if the clock is re-parented to the VIDEO_PLL, changes to the
> > pixel clock have an effect on the PLL ref clock. Therefore, the driver
> > must read and potentially update the PLL ref clock on every modeset.
> >
> > I also found that the rounding mode of the porches and active area has
> > an effect on the working modes. If the driver rounds up instead of
> > rounding down and be calculates them in Hz instead of kHz, more modes
> > start to work.
> >
> > The following table shows the modes that were working in my test without
> > this patch set and the modes that are working now:
> >
> > |            Mode | Before | Now |
> > | 1920x1080-60.00 | X      | X   |
> > | 1920x1080-59.94 |        | X   |
> > | 1920x1080-50.00 |        | X   |
> > | 1920x1080-30.00 |        | X   |
> > | 1920x1080-29.97 |        | X   |
> > | 1920x1080-25.00 |        | X   |
> > | 1920x1080-24.00 |        |     |
> > | 1920x1080-23.98 |        |     |
> > | 1680x1050-59.88 |        | X   |
> > | 1280x1024-75.03 | X      | X   |
> > | 1280x1024-60.02 | X      | X   |
> > |  1200x960-59.99 |        | X   |
> > |  1152x864-75.00 | X      | X   |
> > |  1280x720-60.00 |        |     |
> > |  1280x720-59.94 |        |     |
> > |  1280x720-50.00 |        | X   |
> > |  1024x768-75.03 |        | X   |
> > |  1024x768-60.00 |        | X   |
> > |   800x600-75.00 | X      | X   |
> > |   800x600-60.32 | X      | X   |
> > |   720x576-50.00 | X      | X   |
> > |   720x480-60.00 |        |     |
> > |   720x480-59.94 | X      |     |
> > |   640x480-75.00 | X      | X   |
> > |   640x480-60.00 |        | X   |
> > |   640x480-59.94 |        | X   |
> > |   720x400-70.08 |        |     |
> >
>
> Nice!
>
> > Interestingly, the 720x480-59.94 mode stopped working. However, I am
> > able to bring up the 720x480 modes by manually hacking the active area
> > (hsa) to 40 and carefully adjusting the clocks, but something still
> > seems to be off.
>
> Checkout my
>
> branch: https://github.com/aford173/linux/commit/183cf6d154afeb9b0300500b09d7b8ec53047a12
>
> I found that certain resolutions don't properly round, and it seemed
> to be related to the size of HFP.  HFP of 110 when divded between 4
> lanes, required a round-up, but then I had to recalculate the rest of
> the horizontal timings to compensate.
>
> I was going to push that as an RFC, but I will investigate your patch
> series first.  With my small rounding correction, I am able to get
> 720x480 and 720p on my imx8mp, but not my mini/nano, so I am hoping
> your patch series fixes that issue for me.
>
> >
> > Unfortunately, a few more modes are still not working at all. The NXP
> > downstream kernel has some quirks to handle some of the modes especially
> > wrt. to the porches, but I cannot figure out, what the driver should
> > actually do in these cases. Maybe there is still an error in the
> > calculation of the porches and someone at NXP can chime in.
>
> Hopefully the comment in my above patch explains how the calculation
> is corrected and adjusted to get some of the missing resolutions.

I tested my above patch and it works to sync 720p-60 on my imx8mp, but
it doesn't seem to sync on my imx8mm using the same monitor and HDMI
cable.  I don't have a DSI analyzer, so I might still send out a
modified version of my patch as an RFC once this gets approved.

adam
>
> > Michael
> >
> > Signed-off-by: Michael Tretter <m.tretter@xxxxxxxxxxxxxx>
>
> I'll try to reivew this week and respond with my feedback.
>
> adam
>
> > ---
> > Marco Felsch (1):
> >       drm/bridge: samsung-dsim: add more mipi-dsi device debug information
> >
> > Michael Tretter (4):
> >       drm/bridge: samsung-dsim: reread ref clock before configuring PLL
> >       drm/bridge: samsung-dsim: update PLL reference clock
> >       drm/bridge: samsung-dsim: adjust porches by rounding up
> >       drm/bridge: samsung-dsim: calculate porches in Hz
> >
> >  drivers/gpu/drm/bridge/samsung-dsim.c | 42 +++++++++++++++++++++++++----------
> >  include/drm/bridge/samsung-dsim.h     |  1 +
> >  2 files changed, 31 insertions(+), 12 deletions(-)
> > ---
> > base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
> > change-id: 20230818-samsung-dsim-42346444bce5
> >
> > Best regards,
> > --
> > Michael Tretter <m.tretter@xxxxxxxxxxxxxx>
> >